Bicycle crank arm parts/assembly and assembly tools

ABSTRACT

A tool for fixing a chainwheel to a crank arm assembly of the type wherein a crank axle mounting section of a crank arm mounts to an end of a crank axle. The crank axle mounting section includes a threaded outer surface, and a nut is provided for fixing the chainwheel to the crank axle mounting section. The nut includes a plurality of nut splines disposed on an outer peripheral surface thereof and a threaded inner peripheral surface for meshing with the threaded outer surface of the crank axle mounting section. The tool includes a tool-mount member shaped to be held and turned by a second tool, wherein the tool-mount member defines an opening for receiving the crank axle therethrough. An operating member is formed as one-piece with the tool-mount member and has a plurality of splines extending from an inside surface thereof for meshing with the plurality of nut splines. An auxiliary tool having first and second ends has a grip section disposed in close proximity to the first end, wherein the grip section has a diameter greater than or equal to a diameter of an end of the crank axle. A support section adjacent to the grip section has a diameter less than a diameter of the opening of the tool-mount member so that the support section is fitted within the opening.

This is a division of application Ser. No. 08/687,203 filed Jul. 25,1996 pending.

BACKGROUND OF THE INVENTION

The present invention is directed to a bicycle crank axle, a crank arm,and a crank set that offer high mounting precision and fasteningstrength, and that contribute to lighter weight. It also relates to abolt and assembly tools used for assembling these components.

In conventional mounting mechanisms for the crank arms and crank axle ina bicycle, both ends of the crank axle are shaped into essentiallysquare columns, a square hole is made in each crank arm, and the two arefitted together to fasten the crank arm onto the axle. The precision ofcentering afforded by the conventional mechanism for fitting togetherthe crank arms and the crank axle is inadequate, and the strength of thelinkage in the direction of rotation is inadequate as well. The problemof inadequate linkage strength is particularly notable where an aluminumalloy hollow pipe structure has been adopted for the crank axle, orwhere an aluminum alloy hollow structure has been adopted for the crankarms in order to reduce weight.

SUMMARY OF THE INVENTION

The present invention is directed to a bicycle crank axle, a crank arm,and a crank set that offer high mounting precision and fasteningstrength, but also contribute to lighter weight. Novel bolt and assemblytools used are for installing and removing these components so thatassembly and disassembly may be accomplished very easily.

In one embodiment of the present invention, a crank axle includes anaxle body having first and second ends, a first rotary linkage memberdisposed at the first end of the axle body for nonrotatably fitting afirst crank arm thereto, and a first centering structure disposed at thefirst end of the axle body in close proximity to the first rotarylinkage member. If desired, the rotary linkage member may be formed as aplurality of splines, and the same structure may be formed at the secondend. A crank arm for fitting to the crank axle includes a crank axlemounting section having a centering structure for centering the crankaxle mounting section to an end of a crank axle, and a rotary linkagemember for nonrotatably fitting the crank axle mounting section to theend of the crank axle. If desired, the rotary linkage member for thecrank arm may comprise splines that mesh with splines on the end of thecrank axle. Such a structure provides secure linking of the crank arm tothe crank axle without adding excessive weight.

To facilitate removal of the crank arm, a special bolt is used to fixthe crank arm to the crank axle. The bolt includes a head, a threadedsection having a diameter greater than or equal to the head, and aflange disposed between the head and the threaded section. The flangepreferably has a diameter greater than the diameter of the threadedsection, and the head defines a multiple-sided tool-engaging hole whichextends axially into the threaded section to maximize the tool engagingsurface. The crank axle mounting section of the crank arm preferablyincludes a stop ring or similar structure located so that the flange ofthe bolt is disposed between the stop ring and the first end of the axlebody. As a result, the bolt flange presses the crank arm apart from thecrank axle when the bolt is loosened.

Special tools may be provided to allow easy installation and removal ofthe components. For example, a tool that can be used for both fixing theaxle to the bicycle and fixing a chainwheel to the crank arm includes atool-mount member shaped to be held and turned by a tool, wherein thetool-mount member defines an opening for receiving a portion of the axlebody therethrough. An operating member having a plurality of splinesformed on an inside surface thereof is coupled to the tool-mount member.The splines may engage corresponding splines on a mounting adapter forthe crank axle or corresponding splines on a nut used to fix achainwheel to the crank arm. In the latter case, an auxiliary tool maybe provided to ensure stable operation of the tool. The auxiliary toolmay include a grip section disposed in close proximity to a first endthereof, wherein the grip section has a diameter greater than or equalto a diameter of an end of the crank axle. A support section may bedisposed adjacent to the grip section and sized to fit within theopening in the tool-mount member. A second end of the auxiliary tool hasa threaded inner peripheral surface which can engage with the bolt usedto mount the crank arm to the axle. In this case the bolt serves totemporarily fix the main and auxiliary tool to the crank arm so that themain tool can reliably tighten the chainring fixing nut.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a particular embodiment of a crank armaccording to the present invention;

FIG. 2 is a side view of the crank arm shown in FIG. 1;

FIG. 3 is view taken along line 3--3 in FIG. 1;

FIG. 4 is a rear view of the crank arm shown in FIG. 1;

FIG. 5A-5C are cross sectional views taken along lines 5A--5A, 5B--5BAND 5C--5C, respectively, in FIG. 1;

FIG. 6 is an oblique view of a particular embodiment of a crank axleaccording to the present invention for use with the crank arm shown inFIG. 1;

FIG. 7 is a cross sectional view of right and left side crank armsattached to the crank axle shown in FIG. 6;

FIG. 8 is a cross sectional view illustrating a particular embodiment ofa crank arm assembly according to the present invention including a boltused to fix the crank arms to the crank axle;

FIG. 9 is a partial cross sectional view of alternative embodiment ofthe bolt shown in FIG. 8;

FIG. 10 is an oblique view of the bolt shown in FIG. 9;

FIG. 11 is a partial cross sectional view of a crank axle according tothe present invention mounted to a bicycle frame;

FIG. 12 is a cross sectional view illustrating a main tool and anauxiliary tool according to the present invention used to fixchainwheels to the crank arm shown in FIG. 3;

FIG. 13 is an oblique view of the main tool shown in FIG. 12;

FIG. 14 is an end view of the tool shown in FIG. 13; and

FIG. 15 is a partial cross sectional view of the auxiliary tool shown inFIG. 12.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a front view of a particular embodiment of a crank arm 1according to the present invention. In this embodiment, the crank arm 1is fabricated from an aluminum alloy. As shown in FIG. 1, the crank armend on the pedal mounting side 4 is narrow, and the crank arm end on thecrank axle mounting side 2 is wide. Varying the width of the crank arm 1depending on the position in this way ensures that the stress bearing oncrank arm is essentially constant at any point. A chamfered section 11is formed at the front sides of the crank arm 1. The size of the chamferis greater in proximity to the crank arm end on the crank axle mountingside 2 and becomes continuously smaller towards the crank arm end on thepedal mounting side 4. The front surface of the crank arm 1 can beinscribed with the manufacturer's logo, a trademark indicating theproduct name, or the like using laser marking or other means.

A crank axle mounting hole 21 for mounting the crank arm 1 onto thecrank axle 5 is formed on the crank axle mounting side 2 of the crankarm 1. The crank arm 1 is mounted onto the crank axle 5 using this crankaxle mounting hole 21 as illustrated in FIG. 6. A pedal mounting hole 41is formed at the crank arm end on the pedal mounting side 4 of the crankarm 1. The pedal (not shown) is mounted in this pedal mounting hole 41.

FIG. 2 is a side view of the crank arm shown in FIG. 1, and FIG. 3 is alongitudinal cross sectional view of the crank arm shown in FIG. 1. Asshown in those figures, a groove 31 that extends in the lengthwisedirection is formed on the back surface of the central section 3 of thecrank arm. The shape of the groove 31 is such that in proximity to thetwo ends of the groove 31, the depth of the groove becomes progressivelysmaller towards each end, with the groove depth reaching a minimum ateach end. Thus, the bottom surface of the groove may be termed a "shiphull shape". The bottom surface of the groove 31 in its central sectionis essentially parallel to the front surface of the central section 3 ofthe crank arm.

A stepped section 32 is formed at the open side of the groove 31. A capmember 33 is inserted into this stepped section 32, and the cap member33 is affixed at its perimeter to the body of the crank arm 1 by inertgas welding using argon gas. The front surface of the body of the crankarm 1 and the surface of the cap member 33 are flush. The pad producedin welding should be removed by machining or other means in order tomake the surface flush.

A crank axle mounting hole 21 is formed on the crank axle mounting side2. The inside wall of the crank axle mounting hole 21 has a flange 22that projects inward, and female splines 23 which are contiguous withthe back surface of this flange 22. The section of the crank axlemounting hole 21 located closer to the back surface than the splines 23constitutes the centering member 24. The centering member 24 can bestraight, with an inside diameter that does not vary in the axialdirection, but more commonly has a tapered shape whose inside diameterflares out towards the back. The taper angle is 2° to 3°. Male splines25 for locking the chainring 6 in place are formed on the outerperiphery of the basal portion of the protruding section located on theback surface of the crank arm end of the crank axle mounting side 2. Athread 26 for affixing the chainring 6 is formed on the outer peripheryof the protruding section on the back surface.

FIG. 4 shows the crank arm 1 viewed from the back. As shown in FIG. 4,the splines 23 and 25 each comprise eight teeth. Too few teeth resultsin inadequate linkage strength on the part of the rotary linkage member.Providing too many teeth requires complex machining and entails highercosts, and increases the probability of errors in distribution andpositioning in the direction of rotation.

FIGS. 5A-5C are cross sectional views taken along lines 5A--5A, 5B--5Band 5C--5C, respectively, in FIG. 1. As shown in those figures, thegroove 31 constitutes the majority of the cross section interior in thecentral section 3 of the crank arm in order to decrease the weight.

FIG. 6 shows the exterior of the crank axle 5. Centering members 52A,52Bare formed at each end of the crank axle 5. The centering members52A,52B can be straight, with a diameter that does not vary, but theyusually have a tapered shape which narrows at the ends. The taper angleis 2° to 3°. Male splines 51A,51B are provided further towards the endfrom the centering members 52A,52. The splines 51A,51B have aneight-tooth design. The peripheral surfaces of the splines form acontinuous surface with the peripheral surfaces of the centering members52A,52B. The shape of each spline 51A,51B is basically square, with theplanes of the sides being essentially parallel. The linking force in thedirection of rotation is borne by planes which are essentiallyorthogonal to the direction of force, so chatter is largely eliminated.

The end surfaces of the crank axle 5 are provided with internal threads53 for affixing the crank arms 1. The crank axle 5 is a hollow pipewhose wall is thinner in the central section than at the two ends, asshown in FIG. 7. In this embodiment, an aluminum alloy is used as thematerial for the crank axle 5. This, together with the fact that theaxle is hollow, contributes to reduced weight.

FIG. 7 depicts the crank axle 5, the crank arms 1,100, and the chainring6 in assembled form. The chainring 6 is mounted onto the crank arm 1 onone side, locked in place by the splines 25, and fixed with a nut 61.The crank arm 1 to which the chainring 6 has been affixed is mountedonto one end of the crank axle 5 and affixed by a bolt 54. The crank arm100 without a chainring attached is affixed to the other end of thecrank axle 5. The centering members 24 of the crank arms 1,100 fittightly with the centering members 52A,52B of the crank axle 5 so thatthe components are centered with high precision. The female splines 23of the crank arms 1,100 mesh with the male splines 51A,51B of the crankaxle 5 to afford a linkage having high strength in the direction ofrotation.

The centering members 52A,52 of the aforementioned crank axle 5 and thecentering members 24 of the crank arms 1,100 have tapered junctions, sothe two tapered surfaces fit together tightly. It is therefore necessaryto use a removal tool in order to remove the crank arm 1,100 from thecrank axle 5. However, the alternative embodiment depicted in FIG. 8 isdesigned so that a bolt 54 that fastens the crank axle 5 and the crankarm 1 (or 100) can be used to release the components.

As shown in FIG. 12, an integrated flange 55 is formed on the head ofthe bolt 54. When fastening the crank axle 5 and the crank arm 1together, a washer 56 is inserted and the bolt 54 is tightened. A stopring 58 is inserted into and retained by a groove 57 located on theinside surface of the crank axle mounting hole 21. To remove the crankarm 1 from the crank axle, a hexagonal Allen key is inserted into thehexagonal hole 59 in the crank arm fixing bolt 54 and turned in thereverse direction. The flange 55 of the bolt 54 then pushes the sidesurface of the stop ring 58. The flange 55 thus forces the crank arm 1in the axial direction, so the tight-fitting tapered junctions of thecentering members 52A,52 of the crank axle 5 and the centering members24 of the crank arms 1 can be easily released. Thus, the need for aspecial tool such as an extractor is obviated.

FIG. 9 is a partial cross sectional view of alternative embodiment ofthe bolt shown in FIG. 8, and FIG. 10 is an oblique view of the boltshown in FIG. 9. In the bolt 54 depicted in FIG. 8, the diameter of thethread section and the diameter of the head are about the same, but inthe bolt 54 depicted in FIG. 9 and 10, the diameter of the threadsection 542 is greater than the diameter of the head 541, and thediameter of the flange 55 is greater than the diameter of the threadsection 542. The provision of a thread section 542 with a large diameterensures sufficient strength on the part of the thread section even whenthe component is fabricated from a light alloy such as an aluminumalloy, and affords adequate tightening force on the part of the bolt 54.

A hexagonal hole 59 formed in the center of the end of the head 541extends in the direction of the bolt axis. The hexagonal hole 59 extendsalmost to the distal end of the bolt 54, such that its bottom surface islocated in proximity to the end surface. A longer hexagonal hole 59provides a greater area of contact between the tightening tool (an Allenkey) and the hexagonal hole 59 so that adequate tightening can beachieved even with a light alloy bolt. The length of the hexagonal hole59 can be chosen in accordance with the tightening force required, butit is necessary for the length to be at least such that the bottomsurface of the hexagonal hole 59 extends to the inside surface of thethread section 542. The diameter of the thread section 542 is ratherthick, so the hexagonal hole 59 can extend into its interior; it hasadequate strength even when the hexagonal hole 59 is extended into itsinterior. When fabricated from an aluminum alloy, the bolt 54 has bothlight weight and adequate strength.

FIG. 11 depicts the crank axle 5 which pertains to the present inventioninstalled in the bicycle frame 10. The crank axle 5 pertaining to thisembodiment is provided with a retainer member 50 which protrudes fromthe center of its outside surface for retaining the bearings. To installthe crank axle 5 in the frame 10, a left mounting adapter 101 and aright mounting adapter 102 are threaded between the frame 10 and thecrank axle 5 so that the bearings are retained by the retainer members50. The outsides of the ends of the left mounting adapter 101 and aright mounting adapter 102 are provided with male splines. These malesplines mesh with the female splines of the assembly tool 7 so that eachadapter can be screwed in.

The design of an assembly tool 7 is shown in FIG. 13. The end facing theviewer is provided with an essentially regular hexagonal wrench mountmember 71. A wrench or other tool is fitted over the wrench mount member71, and the entire assembly tool 7 is rotated around its axis. A middlesection 72 is located adjacent to the wrench mount member 71. Theperipheral surface of the middle section 72 is cylindrical, and is cutaway at opposing faces to produce flat surfaces. Tools such as wrenchesof different sizes can be fitted over the flat sections of the middlesection 72. The other end of the assembly tool 7 has a large-diametersection 73.

FIG. 14 shows the assembly tool 7 viewed from the large-diameter section73 side. The inside of the large-diameter section 73 takes the form ofan open cavity. As shown in FIG. 14, female splines 74 are located inthe interior. These female splines 74 mesh with the male splines of theleft mounting adapter 101 and the right mounting adapter 102. Athrough-hole 75 which extends in the axial direction is located in thecenter of the assembly tool 7. The diameter of the through-hole 75 issuch that the end of the crank axle 5 will pass through it. When theleft and right mounting adapters are screwed in, the ends of the crankaxle 5 are passed through the through-holes 75 so that the crank axle 5serves as a guide for rotation of the assembly tool 7, thus facilitatingthe assembly operation.

FIG. 12 shows the crank arm 1 with the chainring 6 attached. Asillustrated in FIG. 12, the chainring 6 is mounted onto the crank armend on the crank axle mounting side 2 of the crank arm 1 and fixed by anut 61. The peripheral surface of the nut 61 is provided with malesplines having the same pitch as the male splines of the left mountingadapter 101 and the right mounting adapter 102, as shown in FIG. 11.Thus, the nut 61 can be tightened using the same assembly tool 7 as thatshown in FIG. 11.

An auxiliary assembly tool 8 is also used in the tightening operation inorder to prevent the assembly tool 7 from coming off during tightening.The design of the auxiliary assembly tool 8 is shown in FIG. 15. One endof the approximately cylindrical auxiliary assembly tool 8 is providedwith a grip section 81 whose outside surface has been knurled to preventslippage. The diameter of the grip section 81 is greater than thediameter of the through-hole 75 of the assembly tool 7, and it isdesigned to retained the assembly tool 7. A inside surface supportsection 82 is formed next to the grip section 81. The diameter of theinside surface support section 82 is about the same as the diameter ofthe end of the crank axle 5. Thus, the inside surface of thethrough-hole 75 in the assembly tool 7 can be rotatably supported by theinside surface support section 82. The other end of the auxiliaryassembly tool 8 is provided with a threaded section 83 into which thebolt 54 can be screwed from the end. The length of the auxiliaryassembly tool 8 has been designed such that when the auxiliary assemblytool 8 has been fixed to the crank arm 1 by the bolt 54, there is aslight gap (about 0.5 mm) between the grip section 81 and the assemblytool 7. Thus, the assembly tool 7 is rotatably supported by theauxiliary assembly tool 8 in such a way that it will not come off fromthe nut 61. Thus, a wrench or other tool can be fitted onto the wrenchmount member 71 and the nut 61 can be tightened to fix the chainring 6to the crank arm 1 while the assembly tool 7 is supported by theauxiliary assembly tool 8. Since the assembly tool 7 is prevented fromcoming off from the nut 61, the operation may be conducted easily andefficiently.

While the above is a description of various embodiments of the presentinvention, further modifications may be employed without departing fromthe spirit and scope of the present invention. For example, in theembodiment shown in FIG. 8, a stop ring 58 was provided in crank arm 1.However, an integrated member which corresponds in function to the stopring 58 may be formed on the crank arm 1 instead of the stop ring 58, orsome other component may be welded on. Thus, the scope of the inventionshould not be limited by the specific structures disclosed. Instead, thetrue scope of the invention should be determined by the followingclaims. Of course, although labeling symbols are used in the claims inorder to facilitate reference to the figures, the present invention isnot intended to be limited to the constructions in the appended figuresby such labeling.

What is claimed is:
 1. A tool for fixing a crank axle (5) to a bicycleframe (10), the crank axle (5) being of the type including an axle bodyhaving a plurality of splines (51) disposed at a first end thereof, thetool comprising:a tool-mount member (71) shaped to be held and turned bya second tool; wherein the tool-mount member (71) defines an opening(75) for receiving the first end of the axle body therethrough; and anoperating member (73) one-piece with the tool-mount member (71) andhaving a plurality of splines (74) extending radially inwardly from aninside surface thereof.
 2. A tool for fixing a chainring to a crank armassembly of the type wherein a crank axle mounting section (21) of acrank arm (1) mounts to an end of a crank axle (5), the crank axlemounting section (21) including a threaded outer surface (26), andwherein a nut (61) is provided for fixing a chainwheel to the crank axlemounting section (21), the nut (61) including a plurality of nut splinesdisposed on an outer peripheral surface thereof and a threaded innerperipheral surface for meshing with the threaded outer surface (26) ofthe crank axle mounting section (21), the tool comprising:a tool-mountmember (71) shaped to be held and turned by a second tool; wherein thetool-mount member (71) defines an opening (75) for receiving the crankaxle (5) therethrough; and an operating member (73) one-piece with thetool-mount member (71) and having a plurality of splines (74) extendingradially inwardly from an inside surface thereof for meshing with theplurality of nut splines.
 3. The tool according to claim 2 furthercomprising:an auxiliary tool (8) having first and second ends, theauxiliary tool (8) including: a grip section (81) disposed in closeproximity to the first end, the grip section (81) having a diametergreater than or equal to a diameter of an end of the crank axle (5); asupport section (82) adjacent to the grip section and having a diameterless than a diameter of the opening (75); wherein the support section(82) is fitted within the opening (75); and wherein the second end has athreaded inner peripheral surface (83).
 4. The tool according to claim 3wherein the grip section (81) has a knurled surface.